1. Field of the Invention
The present invention relates to an internal combustion engine.
2. Description of Related Art
A spark-ignited internal combustion engine has been known in which a variable compression ratio mechanism can change a mechanical compression ratio (see Japanese Patent Application Publication No. 2005-214088 (JP 2005-214088 A)). The variable compression ratio mechanism includes an operation element, an input actuator, and a reverse input torque cutoff clutch. The input actuator generates input torque for moving the operation element. The reverse input torque cutoff clutch is disposed between an output shaft of the input actuator and the operation element. The reverse input torque cutoff clutch is disposed to transmit the input torque from the input actuator to the operation element as well as to cut off the transmission of reverse input torque from the operation element to the input actuator. The variable compression ratio mechanism changes the mechanical compression ratio by the movement of the operation element. The reverse input torque cutoff clutch includes a fixed member, a movable member, clearance, a wedge member, and a moving member. The movable member is rotatable with respect to the fixed member. The clearance is defined by a peripheral surface of the fixed member and a peripheral surface of the movable member and is annular. The wedge member is movably disposed in the clearance. The moving member moves the wedge member in the clearance. The output shaft of the input actuator is connected to the movable member with clearance in a rotational direction thereof. The operation element is also connected to the movable member. The output shaft of the input actuator is connected to the moving member. The moving member moves in the clearance in a same direction as the rotational direction of the output shaft of the input actuator. The clearance is formed with a rotation prevention area and a rotation allowable area. The rotation prevention area is located on an upstream side of the rotation allowable area in a reverse input torque acting direction. The rotation prevention area prevents the movable member from rotating in the reverse input torque acting direction as the wedge member abuts against both of the fixed member and the movable member. The rotation allowable area allows the movable member to rotate in the reverse input torque acting direction. When the movable member moves in the reverse input torque acting direction to change the mechanical compression ratio, the input actuator first rotates in the reverse input torque acting direction. This causes the wedge member to move from the rotation prevention area to the rotation allowable area without rotating the movable member. Then, the input actuator further rotates in the reverse input torque acting direction. This causes the movable member to further rotate in the reverse input torque acting direction. Accordingly, the operation element moves to change the mechanical compression ratio.
In other words, the movable member is locked when the wedge member is in the rotation prevention area, and the movable member is unlocked when the wedge member moves to the rotation allowable area. In this case, a direction of the movement of the wedge member that is necessary to unlock the movable member is set to be the same as the reverse input torque acting direction in JP 2005-214088 A. The input actuator rotates the movable member to an angular position where a desired mechanical compression ratio can be obtained in a state that the movable member is unlocked.
The reverse input torque acts on the movable member as soon as the movable member is unlocked. Consequently, the reverse input torque causes the movable member to rotate with respect to the wedge member. Accordingly, the wedge member returns to locate in the rotation prevention area again. In other words, there is a possibility that the movable member is relocked. If the movable member is relocked, the movable member may not rotate smoothly, and thus the mechanical compression ratio may not be changed smoothly. In addition, there is a possibility of generating undesirable noise and vibration upon relocking.